The invention relates to a process of manufacturing a circuit including a first circuit plane composed of a ceramic substrate which is covered with, for example, thick-film structures and imprinted with corresponding conductor paths having contact faces.
Increasing requirements for the complexity of future hybrid circuits and the demand for short circuit path lengths can be realized only with multi-layer circuits. New processes have been developed due to process specific drawbacks, particularly due to geometrical limitations as a result of uneven topography and curvatures of the substrate and due to decreasing yields as a result of the high number of process steps in multi-layer thick-film circuits equipped with printed-on dielectric materials. These processes include the so-called green tape process. In this green tape or green sheet process, unsintered ceramic sheets are imprinted with switching elements and conductor paths, generally assembled into a multi-layer element, pressed and sintered. The development of these low-temperature sintering (at approximately 850.degree. C.) glass ceramic sheets permits the realization of highly complex multi-layer circuits with high yields.
On the other hand, the thermal conductivity of these multi-layer circuits lies at only about 15% of a ceramic element composed, for example, of Al.sub.2 O.sub.3. Likewise, its mechanical strength lies below that of an Al.sub.2 O.sub.3 ceramic, namely even below half the strength. Therefore, these green tape circuits are not well suited for robust use in the electronic systems of automobiles.